In recent years, balloon catheters have been used for improving lesion affected areas (stenosed parts) generated in body lumens. A balloon catheter can include an elongate shaft portion, and a balloon, which is provided on the distal side of the shaft portion and is inflatable in the radial direction. After the balloon in a deflated state is brought to a target site in the body by way of a thin body lumen, the balloon is inflated, whereby the lesion affected area can be pushed wide open.
If a lesion affected area is forcibly pushed open, however, excessive proliferation of endothelial cells may occur, causing new stenosis (restenosis). In view of this, recently, drug eluting balloons wherein an outer surface of a balloon is coated with a drug for restraining stenosis have been used. The drug eluting balloon, by being inflated, is able to instantaneously release the drug contained in the coating on the outer surface of the drug eluting balloon to the lesion affected area and transfer the drug to the living body tissue, thereby restraining restenosis.
A variety of methods have been proposed for coating a balloon with a drug. For instance, U.S. Patent Application Publication No. 2010/055294 describes a method in which a coating liquid containing a drug is supplied to a surface of a balloon while the coating quantity is being controlled and the balloon is being rotated and being moved in an axial direction, and the coating liquid is dried to form a coating layer containing the drug.
If the balloon is bent along the axial direction when the balloon surface is coated with the drug while being rotated, the balloon gets eccentric when the balloon is rotated. The bending of the balloon arises from differences between the balloon and a shaft portion in material and/or thickness, variations in expansion/contraction ratio from part to part upon inflation of the balloon, and the like. The influence of bending is great especially in a balloon that is long in the axial direction. When the balloon is bent to get eccentric, the distance from the distal end of a dispensing tube for supplying the coating liquid to the outer surface of the rotating balloon varies with rotation, making it difficult to uniformly coat the outer surface of the balloon with the drug. Further, the drug in the coating on the outer surface of the balloon can assume different morphological forms such as crystalline form, amorphous form and mixed forms thereof depending on the length of time of volatilization of the solvent, etc. When it becomes difficult to achieve uniform coating with the drug, the volatilization of the solvent may become non-uniform, possibly making it difficult to control the formation of the morphological form. Neither of the crystalline form and the amorphous form is more desirable than the other, and it can be desirable that the morphological form of the drug can be selected according to the purpose